Addison's Disease

Addison's disease (hypoadrenocorticism) occurs when the adrenal glands fail to produce sufficient cortisol and, in the classic form, aldosterone. Cortisol helps the body manage stress and maintain normal metabolism; aldosterone regulates sodium and potassium balance. Deficiency of both causes the characteristic waxing and waning signs that lead to the condition being called "the great imitator."

Most cases are idiopathic (immune-mediated destruction of the adrenal cortex). Some occur as a consequence of stopping long-term steroid therapy too quickly. A rare atypical form involves only cortisol deficiency (no aldosterone deficiency) and is harder to diagnose.

Signs to watch for

Addison's signs are non-specific and episodic, which is why diagnosis is often delayed. Dogs may have "bad days" that resolve spontaneously - which are actually episodes where cortisol demand briefly exceeds production.

Log the following when you notice them:

GI signs: Vomiting, diarrhoea, loss of appetite - often the most prominent episodic signs

Lethargy and weakness: Disproportionate tiredness, difficulty rising, general quietness

Weight loss: Usually gradual across multiple episodes

Shaking or trembling: Particularly in the legs

Increased thirst/urination: Less common than in Cushing's but may be present

Abdominal pain: Occasionally observed

These signs often resolve partially, then recur - the "waxing and waning" pattern is characteristic and often noted in retrospect after diagnosis.

The Addisonian crisis

When physiological demand for cortisol exceeds what the damaged adrenal glands can produce - typically triggered by stress, illness, or injury - an acute Addisonian crisis occurs. This is a life-threatening emergency:

• Severe weakness or collapse
• Profound lethargy (inability to stand)
• Severe vomiting and diarrhoea
• Bradycardia (slow heart rate) - dangerous and requires emergency treatment
• Hypovolaemic shock

Any dog showing these signs requires immediate emergency veterinary care. The crisis is treated with IV fluids, IV glucocorticoids, and mineralocorticoid replacement.

Diagnosis

Diagnosis is via the ACTH stimulation test - cortisol is measured before and after an ACTH injection. In a dog with Addison's, cortisol fails to rise appropriately. Baseline electrolyte measurements (low sodium, high potassium) suggest mineralocorticoid deficiency.

Treatment

Addison's disease is managed, not cured, but with good management most dogs live entirely normal lives.

Typical ongoing treatment:

• Mineralocorticoid replacement: Desoxycorticosterone pivalate (DOCP, Zycortal) - injectable, given every 25–28 days; or fludrocortisone (oral, daily)
• Glucocorticoid replacement: Prednisolone - daily, at a low maintenance dose

Stress dosing: In any situation of significant physical or emotional stress (illness, surgery, trauma, fireworks, a major change), the glucocorticoid dose must be increased to 3–5 times the maintenance dose. This is critical - failing to increase the dose in stressful situations can precipitate a crisis even in a well-controlled dog.

Log every dose given, every dose increase, and the circumstances prompting the increase.

What to monitor

Weekly observations to log:

• Appetite (full, partial, or absent)
• Energy level
• GI signs (vomiting, diarrhoea)
• Water intake
• Any stressful events that required dose adjustment

At-clinic monitoring:

• Sodium and potassium electrolytes - measured initially monthly, then every 6 months when stable
• ACTH stimulation - used to assess adequacy of glucocorticoid replacement

When to contact your vet

Go to the emergency vet immediately if:

• Collapse, severe weakness, or inability to stand
• Repeated vomiting and profound lethargy
• Signs of an Addisonian crisis

Contact your vet the same day if:

• Vomiting or diarrhoea accompanied by lethargy in an Addisonian dog - stress dose and vet call together
• Signs are recurring despite treatment

Schedule routine monitoring for:

• Monthly electrolytes initially, then 6-monthly when stable
• Every DOCP injection administration

Frequently Asked Questions

Once diagnosed and treated, will my dog be normal? Yes, in most cases. Addison's disease is one of the more rewarding diagnoses in veterinary medicine - once the diagnosis is made and appropriate replacement therapy is in place, most dogs recover completely and have entirely normal energy, appetite, and quality of life.

What happens if I forget the DOCP injection? The mineralocorticoid effect of DOCP lasts approximately 25–28 days, so slight delays are usually tolerable. If you're more than a few days late, contact your vet. Monitor electrolytes if the injection is significantly delayed, as electrolyte imbalances can develop.

Does my dog need to wear a medical ID tag? Many owners of Addisonian dogs use a medical ID tag stating "Addison's Disease - needs steroids if collapsed." In an emergency where the dog collapses and cannot be identified, this information may prompt the treating vet to administer glucocorticoids which could be life-saving.

My dog has a dental procedure coming up - should I adjust the medication? Yes. Anaesthesia and surgery constitute a significant stressor. The glucocorticoid dose should be increased to the stress dose before and during the procedure. Inform the anaesthetist that your dog has Addison's disease - they will need to plan for this.

Can Addison's be confused with Cushing's? The two conditions cause cortisol abnormalities in opposite directions (Addison's = too little, Cushing's = too much), and the signs are quite different. However, atypical Addison's (cortisol-only deficiency) can mimic Cushing's on some screening tests. A thorough diagnostic work-up differentiates them.